There are many commercial and industrial environments where engines or other vibration inducing mechanisms are supported at relatively fixed structure with some type of vibration damping system interposed between the support structure and the vibrating mechanism. For example, internal combustion engine driven vehicles are provided with shock absorbing engine mounts which are intended to limit the transmission of engine vibrations into the vehicle body frame and vice versa.
Certain prior art vehicle engine mounts comprise elastically deformable hard rubber cushions or the like for cushioning the transfer of vibrations between the engine and the vehicle frame. Such solid elastically deformable engine mounts do help isolate the vehicle body frame carrying the engine from engine induced mechanical vibrations and the engine from vehicle induced vibrations. However, such engine mounts suffer from disadvantages in that they are unable to attenuate the wide range of mechanical vibrations experienced in use on an automobile. For example, an automobile is designed to operate under many speed, torque, acceleration and deceleration conditions, all of which create different mechanical vibration force, frequency and amplitude patterns. The above-mentioned conventional shock absorber type engine mounts are preset and passive in that they only passively react to vibration forces based on their preset elastic design characteristics. Such vibration isolation mounts can be designed to operate quite well over certain narrow mechanical vibration patterns. However, it is impractical, if not impossible, to design effective preset passive isolation vibration mounts which can attenuate vibrations over all operating ranges of the engine and vehicle.
Certain other prior art vehicle engine mounts utilize a closed fluid shock absorber system for cushioning the transfer of vibrations between the engine and the vehicle frame. Since these fluid shock absorber mounts are closed systems, they act much like the elastically deformable spring or hard rubber cushion mounts discussed above. Further, in cases of large relative movement between the parts being supported, the shock attenuation substantially diminishes as the fluid pressure rises. Although certain shock absorber mounts provide for multiple fluid chambers and different flow paths depending upon the relative displacement of the parts being supported, such systems are very complex and costly to construct and are also ultimately limited by the total volume of fluid and fluid accommodating space in the overall closed system at an individual shock absorber mount.
The above-mentioned prior art arrangements thus permit an unacceptable level of transfer of vibration forces between the engine and the vehicle frame, and/or involve very complicated, expensive and space wasting constructions.
The mechanical vibration problems of internal combustion engine driven automotive vehicles discussed above are but one example of complex mechanical vibration problems that occur. Another example is a drive assembly support for the rotor blades of a helicopter. Such helicopter rotor blade drive assemblies further compound the mechanical vibrations that should be attenuated. Prior attempts to attenuate vibrating force transfers between helicopter blade drive assemblies and the helicopter body or helicopter passenger compartment meet with similar difficulties as described above for the motor vehicles driving on the ground, due again to the wide spectrum of vibration force, frequency and amplitude which are experienced during the helicopter operation. Mechanical vibration isolation problems also occur in stationary engine environments such as driving engines for heating and air conditioning units mounted on commercial buildings or stationary engine electrical generators used at construction sites and at remote areas where electric power must be generated. In these installations, it is desired to minimize mechanical vibration force transfers between the engine and pumps or generators driven by same so as to minimize noise and minimize vibration induced mechanical failures.
An exemplary environment where reduction of mechanical vibration transfer is especially desired involves so-called top floor "penthouse" spaces of large commercial buildings with rooftop heating, venting and air conditioning systems (HVAC systems). Due to vibration induced sound and actual vibration movement of the floors and walls caused by the rooftop HVAC systems, top floors of such buildings are not desirable prime office or living spaces. Again, prior attempts to passively mount the large generators, pumps, etc, for such HVAC systems can only imperfectly and inefficiently respond to the induced mechanical vibration and especially to changes in the vibration spectrum occurring during operations.